In recent years, in digital broadcast and the like based on CS and BS, MPEG (Moving Picture Experts Group) technique is adopted as an encoding technique for compressing image data, audio data, and the like. Therefore, a reception device and a recording/reproduction device for digital broadcast and the like need to comprise a device which decodes a bit stream of data that is compression-encoded by MPEG technique.
Now, MPEG2 technique, which is mainly used in a digital broadcast, will be briefly described. In MPEG2 technique, a bit stream of compression-encoded image data, audio data, and the like is referred to as an elementary stream (ES). As a packet structure for carrying this elementary stream, PES (Packetized Elementary Stream) is defined. FIG. 15 is a diagram illustrating a detailed structure of a PES packet. Further, in MPEG2 technique, a PES packet is split into a predetermined unit, stored in a transport stream packet (hereafter, referred to as a “TS packet”), and broadcasted. FIG. 16 is a diagram illustrating a detailed structure of a TS packet. FIG. 17 is a diagram describing the relationship between TS packets and PES data.
For this reason, a device handling a bit stream under MPEG2 technique needs to perform a packet process, i.e., extracting PES data from a plurality of TS packets and decoding it. Hereinafter, this packet process will be described.
FIG. 18 is a block diagram illustrating an exemplary construction of a MPEG decoding device performing a conventional packet process. In FIG. 18, a conventional MPEG decoding device 101 comprises a TS header analyzing section 111, a PES extracting section 112, a PES buffer 113, a PES buffer controlling section 114, and a MPEG decode section 120. The TS header analyzing section 111, the PES extracting section 112, the PES buffer 113, and the PES buffer controlling section 114 together constitute a transport stream decoding section 110.
To the TS header analyzing section 111 and the PES extracting section 112, TS packets under MPEG2 technique are sequentially inputted. Every time when a TS packet is inputted, the TS header analyzing section 111 analyzes the TS header of the TS packet. By referring to the analysis result of the TS header from the TS header analyzing section 111, the PES extracting section 112 extracts necessary PES data from the inputted TS packet. Then, the PES extracting section 112 outputs the extracted PES data to the PES buffer 113. The PES buffer 113 temporarily stores the PES data extracted in the PES extracting section 112. The PES buffer controlling section 114 outputs a control signal to the PES buffer 113 and performs an address control, an accumulated data control, and the like for the PES buffer 113.
The MPEG decode section 120 reads out the PES data from the PES buffer 113 with an arbitrary timing, executes a decode process, and outputs a decoded image and decoded audio. At this time, in order to analyze the PES header necessary for the MPEG decode process, a start position of the PES data, namely, information defining the PES data including the PES header becomes necessary. Therefore, usually, by detecting a packet start code possessed by a PES header in the PES data stored in the PES buffer 113, the MPEG decode section 120 identifies a start position of the PES data. The technology relating to the identification of a start position in PES data is described, for example, in Japanese Laid-Open Patent Publication No. 2001-16547 (pages 6 to 8, FIG. 1).